Denitrification of aquarium water

ABSTRACT

The invention relates to agents for the removal or reduction of inorganic nitrogen compounds, especially nitrate, from biological aquarium waters, containing a biologically degradable polymer, preferably polycaprolactone (PCL) and to the utilization of said agents.

[0001] The invention relates to agents for the removal or reduction ofinorganic nitrogen compounds, in particular nitrate, from biologicalcontainer waters containing a biologically degradable polymer,preferably polycaprolactone (PCL) and to the use of these agents.

[0002] The daily feeding of fish and other water organisms causes aregular introduction of organic nitrogen compounds in aquarium systems.

[0003] In the primarily aerobically operating filtering systems, theintroduced or eliminated organic nitrogen compounds are degraded to formnitrate by the intermediary steps ammonia/ammonium and nitrite whoseconcentration remains low.

[0004] Since the denitrification activity is considerably lower in mostcases than the nitrification activity in the aquarium systems, thisresults in a continuous increase in the nitrate concentration.

[0005] Although the nitrate anion is only very slightly toxic for fish,endeavours are nevertheless made to slow down the increase in nitrate orto keep the nitrate concentration low.

[0006] In addition to ion exchange processes for reducing the nitratewhich, however, produce secondary undesirable effects, the process ofdenitrification is used. The denitrification is associated with largelyanaerobic conditions and the presence of degradable carbon compounds.

[0007] Since the formation of nitrate by nitrification occurs almostcontinuously, it is expedient to also allow the denitrification to takeplace more or less continuously. The amount of nitrate being added dailyin only a low concentration also makes it possible to omit largesubstance conversions during denitrification. Therefore, difficult todissolve organic, biologically degradable polymers are very well suitedas slowly reacting C sources.

[0008] To date, the following processes are known which use the BDPs(biologically degradable polymers):

[0009] a) Granulated material and molded/shaped parts consisting ofpolyhydroxybutyrates (PHB) which are placed in the ground on the bottomof the aquariums to create anaerobic degradation conditions. PHB isbuilt up by special bacterial species as an energy reserve substance andembedded in the cells. Therefore, as natural material, it is easilydegradable. Other BDPs were not used in aquarium systems.

[0010] b) Boley, Müller et al. placed granulated PHB andpolycaprolactone (PCL) in special anaerobic reactors under strictanaerobic reaction conditions which only have a very small flow (0.3-0.5l/h) for the O₂ limiting to degrade nitrate. The amounts of granulatedmaterial used were about 280-380 g per 100 l, i.e. they were very high.

[0011] In comparison to the prior art, the agents, materials orprocesses according to the invention offer considerable advantagesand/or also surprising functional and mechanical improvements for aperson skilled in the field.

[0012] In comparison to the described prior art, the use of granulatedmaterial consisting of polycaprolactone (PCL) offers the followingserious advantages:

[0013] Considerably better industrial availability, since there is nomass producer for PHB at this time.

[0014] Substantial cost advantages, since PHB is about 2 to 3.5 timesmore expensive than PCL.

[0015] In addition, it was surprisingly found that PCL as asynthetic-chemically produced material is similarly easily degradable asPHB.

[0016] PCL exhibits a surprisingly different degradation behaviourcompared to PHB when nitrate is removed in that it already results in acompletely sufficient nitrate reduction under non-anaerobic or evenunder aerobic conditions for aquarium conditions.

[0017] When using PCL granulated material, it was surprisingly shownthat it was just under aerobic operating conditions that a quicker, moreeffective nitrate reduction is obtained than under anaerobic conditions.This fact is surprising and could not be expected with conventional BDPsaccording to the prior art.

[0018] Although it is already known according to the prior art to mixgranulated material and molded bodies consisting of PHB with the bottomlayer of aquariums for a reduction in nitrates, the use of PCLgranulated material in the bottom layer of aquarium systems was notcarried out to date.

[0019] From known or compiled results from experiments with PHBgranulated material, a reaction behaviour similar for PCL (as BDP) wasexpected, namely

[0020] a) the degradation of nitrate by denitrification under preferablyanaerobic conditions in the bottom,

[0021] b) an increase, promotion of the denitrification with thecreation of largely anaerobic conditions.

[0022] However, surprisingly, it was found that PCL in the bottomdegrades nitrate all the more effectively the more coarse-grained thebottom layer is made.

[0023] In a comparative test, 70 g PCL granulated material (round tooval balls, diameter of about 4 mm, content >99% polycaprolactone) per100 l aquarium water were mixed in aquariums with 10 to 20 l bottommatter consisting of

[0024] a) sand (<1 mm)

[0025] b) fine gravel (ø 1-2 mm)

[0026] c) medium coarse gravel (ø 2-3 mm)

[0027] and the increase in nitrate of the aquarium occupied by fish andfed daily was measured over a period of 3 months.

[0028] An Aquarium Not Treated with PCL was Used as a Comparison.

[0029] The following gradation of the test results according to theprior art was suprising and an opposite trend would have been expected:

[0030] a) Sand (ø 1 mm)

[0031] The nitrate content increased in the control aquarium in the testperiod from 49 mg/l to 128 mg/l; only a low decrease in nitrates wasfound in the aquarium treated with PCL. The nitrate increased from 49mg/l to 109 mg/l.

[0032] b) Fine gravel (ø 1-2 mm)

[0033] The nitrate degradation was considerably more intense.

[0034] The nitrate concentration increased from 49 mg/l at the start to74 mg/l, in the control test to 135 mg/l.

[0035] c) Medium coarse gravel (ø 2-3 mm)

[0036] In this case, the nitrate reduction was even more clearlypronounced:

[0037] From 49 mg/l at the start, a decrease in nitrate to only 40 mg/lcould even be seen; in the control test, an increase to 136 mg/l.

[0038] A further experiment with gravel having a particle size of 3-5 mmresulted in a nitrate increase of 18 mg/l at the start to 33 mg/l after3 months, while the control exhibited the following nitrateconcentrations: 18 mg/l to 104 mg/l. The resultant nitrate concentrationwas still under the value for medium coarse gravel (ø 2-3 mm).

[0039] In contrast to the control aquariums not treated in which thenitrate content increased further, the nitrate content remained constantin the PCL-treated aquariums after about 2-3 months, at a leveldependent on the PCL dosage.

[0040] If PCL granulated material of about 4 mm in diameter are mixed infine (ø 1-2 mm), even better in medium coarse (ø 2-3 mm) or even coarsegravel (ø 3-5 mm), the following nitrate concentrations set in in thetreated aquariums, dependent on the bottom layer mixture, with variousPCL dosages in the period of 3 months:

[0041] 1) Various types of bottom mixtures, PCL dosage: 70 g/100 lwater:

[0042] a) sand (ø<1 mm)—increase from 49 to 109 mg/l NO₃

[0043] b) fine gravel (ø 1-2 mm) increase from 49 to 74 mg/l NO₃

[0044] c) medium coarse gravel (ø 2-3 mm)—constant until decline in therange 47 over 27 to 40 mg/l NO₃

[0045] d) coarse gravel (ø 3-5 mm)—increase from 18 to 33 mg/l NO₃ ⁻

[0046] 2. Coarse gravel (ø 3-5 mm) with various PCL dosages after 3months:

[0047] a) 0 g/100 l PCL: increase from 18 mg/l to 104 mg/l NO₃ ⁻

[0048] b) 25 g/100 l PCL: increase from 18 mg/l to 86 mg/l NO₃ ⁻

[0049] c) 50 g/100 l PCL: increase from 18 mg/l to 60 mg/l NO₃ ⁻

[0050] d) 100 g/100 l PCL: reduction from 18 mg/l to 8 mg/l NO₃ ⁻

[0051] The process according to the invention for nitrate limiting,control and reduction by mixing PCL granulated material with fine tocoarse gravel can be carried out very easily by simply mixing the PCLgranulated material in the bottom mixture of the aquarium system.

[0052] The application only has to be repeated every 6-12 months. Itacts advantageously on the water quality, that anaerobic conditions inthe coarse-grained bottom layer mixture that is thoroughly flowedthrough by water are not required and are also not produced by theprocess. As a result, anaerobic decomposition processes and the H₂Srelease by sulfate reduction can be avoided.

[0053] The growth of the water plants rooting in the bottom layermixture is not negatively affected by this, but even clearly promoted.

[0054] The following dosages of PCL granulated material (ø about 4 mm)have shown to be advantageous for mixing in fine to coarse gravel,namely 20 g/100 l water to 200 g/100 l water, preferably 60-120 g/100 lwater.

[0055] Since PCL is not dependent on anaerobic reaction conditions, theuse of PCL granulated material in aerobic filtering systems is alsopossible.

[0056] According to the aforementioned prior art, PCL granulatedmaterial were used in the mixture with PHB granulated material inanaerobic reactors operating in the secondary flow with a very smallflow (0.3-0.5 l/h) and high dosage (280-380 g/100 l) for the anaerobicnitrate degradation.

[0057] It was therefore highly surprising and, according to the priorart, completely unexpected that PCL granulated material (ø about 4 mm)can also be used advantageously under aerobic conditions, i.e. infiltering chambers or filtering units in the main stream (with O₂saturated water) at high flow rates of 20-500 l/h to lower nitrate andeven ammonium and nitrite in aquarium systems.

[0058] However, the use of PCL granulated material as sole filteringmedium in the filter chamber of an inner filter was shown to beunsuitable, since a considerable decrease of the flow rate could alreadybe ascertained after about 2 to 4 weeks, so that a filtering functionwas no longer given. The cause was the formation of slime about thegranular particles which ultimately resulted in the formation of analmost water-impermeable, agglutinated filter filling consisting ofslime-coalesced PCL.

[0059] Although nitrate was removed from the aquarium water at thebeginning by the application described above, it was only as long as thefilter still showed a flow, i.e. after about 2 to 4 weeks, the nitrateremoval also ceased for the aforementioned reasons.

[0060] However, if the PCL granulated material are diluted by anaddition of 25-75% by volume of gravel, preferably having a particlesize of 2-5 mm, and mixing it thoroughly, a filter material is obtainedwhich no longer exhibits the functional problems appearing with pure PCLgranulated material. The filtering chamber of an inner filter was filledwith a 50:50 mixture and the long-term behavior observed. The filteringeffect and the nitrate degradation remained problem-free over a periodof months.

[0061] The described PCL/gravel mixture should also be suitable forfilling other filtering systems as a filtering material, e.g. outerfilter, inner filter with filter chambers, pot filter systems, etc.Advantages of these filtering mixtures are:

[0062] no agglutination by binding slime

[0063] double filtering effect, namely normal biological filtering plusnitrate degradation

[0064] simple exchange when the nitrate degradation is exhausted.

[0065] Instead of gravel, any other commercial filter granulatedmaterial consisting of natural substances such as pumice, sandstone,basalt, etc. or of synthetic materials can, of course, also be used asdilutant for PCL granulated material in filtering chambers.

[0066] The aforementioned problems when using pure PCL granulatedmaterial were also not found when using PCL granulated material infleece filter bags. In this case, the filter bags were only partiallyfilled with about 20-60% of the overall volume and renewed every 4weeks. Since it is very easy to exchange such filter bags and only asmall fraction of the PCL granulated material is degraded in 4 weeks,the PCL dosage is kept almost constant and thus also the rate ofdosage-dependent nitrate reduction.

[0067] The dosages of the PCL granulated material in the application ofthe invention are considerably less than according to the prior art.

[0068] Even 20-40 g/100 l, 35 g/100 l in the experiment, are alreadysufficient to limit the increase in nitrate to 50-60 mg/l. Higherdosages (up to 100 g/100 l) are still considerably more efficient.

[0069] In addition to nitrate, ammonium and nitrite are also effectivelyremoved from the aquarium system in this case.

[0070] When using 100-250 g PCL/100 l, existing ammonium and nitriteconcentrations were reduced to almost 0 mg/l within 0.5 to 1.0 weeks.

[0071] To reduce the nitrate concentration, the following experimentswere performed:

[0072] PCL granulated material were inserted in various dosages inwater-permeable fleece bags in the main filter flow. The water flow was30-1000 l/h, preferably 50-500 l/h.

[0073] 35 g, 70 g and 105 g PCL were filled into the fleece bags per 100l.

[0074] During the test time of 3 months, the following nitrateconcentrations appeared:

[0075] a) control (0 g/100 l PCL)—increase in nitrate from 26 mg/l to175 mg/l,

[0076] b) 35 g/100 l PCL—increase in nitrate from 26 mg/l to 62 mg/l,

[0077] c) 70 g/100 l PCL—decrease in nitrate from 26 mg/l to 20 mg/l,

[0078] d) 105 g/100 l PCL—decrease in nitrate from 26 mg/l to 12 mg/l.

[0079] The documented influence of the nitrate concentrations wereobtained even though nitrate was constantly formed over thenitrification by feeding the fish occupants (see control as comparison)and even though the water conditions remained constantly in the aerobicrange.

[0080] The aerobic character of the nitrate reduction method can also befound in the sulfate reduction not observed in our studies. The sulfatecontent changes in the same manner in all test variations:

[0081] a) control (0 g/100 l PCL)−113 mg/l to 146 mg/l,

[0082] b) 35 g/100 l PCL−115 mg/l to 144 mg/l,

[0083] c) 70 g/100 l PCL−115 mg/l to 142 mg/l,

[0084] d) 105 g/100 l PCL−114 26 mg/l to 143 mg/l.

[0085] A further positive effect of the water treatment with PCLgranulated material was ascertained during the biological activation ofthe nitrification.

[0086] Experiments to Decrease the Ammonia and Nitrite Concentration:

[0087] In the PCL aquariums, the highest intermediate concentrations ofammonia and nitrite were a slightly to clearly less than in theuntreated control.

[0088] The positive side effect of the reduction in NH₄ ⁺ and NO₂ ²⁻concentrations can be clearly intensified with higher PCL dosages.

[0089] If higher PCL dosages are used in the fleece bags which were alsoused in the nitrate reduction, existing NH₄ ⁺ and NO₂ ⁻ concentrations(e.g. 0.25 mMol/l) can be quickly reduced to almost 0 and the formationof increased NH₄₊ and NO₂ ⁻ concentrations, e.g. during the activationphase from newly set up aquariums, can be pushed back.

[0090] This is associated with a substantial improvement of the waterquality for water organisms.

[0091] Dependent on the dosage, the following surprisingly good resultscan be obtained:

[0092] a) 120 g/100 l PCL: 5.0-6.0 mg/l NH₄ ⁺ and 9.0-10.0 mg/l NO₂ ⁻are completely eliminated within a week,

[0093] b) 240 g/100 l PCL: 5.0 mg/l NH₄ ⁺ are almost completelyeliminated within 0.5 weeks, 12.0 mg/l NO₂ ⁻ within 0.5-1 week.

[0094] The danger to fish feared to date when setting up new aquariumsdue to intermediately appearing maximum concentrations of ammonium andnitrite can be overcome by a suitable treatment with PCL.

[0095] During the first 4-6 weeks, about 100-250 g/100 l PCL, preferably120-180 g/100 l PCL, are inserted into the filter.

[0096] Fish-endangering NH₄ ⁺ and NO₂ ⁻ concentrations are therebysafely avoided. In addition, excessive nitrate concentrations (e.g.25-100 mg/l NO₃ ⁻) prevailing in the initial water are also quicklyreduced in this phase.

[0097] After 6 weeks, the natural nitrification has ceased. NH₄ ⁺ andNO₂ ⁻ concentration peaks should then also no longer be feared withreduced PCL amounts (as used for the nitrate reduction).

[0098] The PCL dosage can then be reduced to values, e.g. 50-80 g/100 l,which are sufficient for the remaining minimization of the nitratelevel.

[0099] Further Effects of the Treatment of Aquarian Systems with PCL:

[0100] In addition to the agents, processes and methods according to theinvention described under 3 for a reduction in the concentration orelimination of nitrate and other inorganic species (NH₄ ⁺/NH₃ and NO₂⁻), further effects were observed (chemically and biologically) whichcontribute to promote the water organisms and stabilize the waterchemistry:

[0101] 1. stabilization of the carbonate hardness and thus the pHvalue/range,

[0102] 2. release of CO₂ by continuous oxidation of PCL (by 02 and/ornitrate),

[0103] 3. promotion of water plant growth and nitrification, and

[0104] 4. low to moderate reduction of the phosphate concentration.

[0105] Areas of Application for the Agents and Processes of theInvention

[0106] Due to the very good tolerance and the very low toxicity of PCL,the following areas of application are feasible:

[0107] 1. reparation of aquarian water (freshwater and salt water) inthe home and professional area.

[0108] 2. Preparation of garden pond water.

[0109] 3. Preparation of water in aquaterriums, e.g. to hold watertortoises.

[0110] 4. Rehabilitating eutrophied natural waters.

[0111] 5. Preparing freshwater and salt walter in large aquariums,basins, ponds, tanks in public aquariums, zoos, in intensive fishfarming, in shrimp breeding and culture.

[0112] 6. Preparing N/ammonia rich waste waters from the milk, meat,food industry, brewery, agriculture (animal husbandry), leather industryand other industrial branches with comparable waste water problems.

[0113] Generally, excessive inorganic N compounds can be eliminated fromall waters. The purified waters have an increased water quality andorganism as well as waste water and environmental compatibility.

[0114] Summary of the Agents and Processes According to the Invention

[0115] Agents According to the Invention

[0116] Advantageously, granulated material of polycaprolactone,purity >99%, about 4 mm, are used.

[0117] However, all technologically appropriate production variationscan also be used, such as e.g. injection molds which can be made of PCL,e.g.

[0118] spheres, cylinders, cubes, rectangular parallelipipeds, interalia smooth or with any inner and outer surface structure desired,

[0119] extruded parts, such as e.g. rods, fibers, webs, hollow tubes andalso hollow profiles,

[0120] blow molds, such as hoses, films, etc.

[0121] Processes According to the Invention

[0122] The PCL bodies obtained are used in the water of aquarian systemsand other water systems according to the dosage particulars defined inthe description to reduce the nitrate, ammonia and nitriteconcentration.

[0123] Mixing with Gravel or Bottom in General

[0124] PCL granulated material, molded bodies in the dosage 20 g/100 lto 200 g/100 l water, preferably 60 g/100 l to 120 g/100 l water, aremixed in the gravel having a particle size of 2-6 mm in order to lowerand stabilize the nitrate content to low or lower concentrations.

[0125] Use in Filtering Systems

[0126] PCL granulated material, molded bodies are used in the mainstream of filters (flow 30-1000 l/h, preferably 50-500 l/h) in filterchambers, fleece bags, gauze bags or other water-permeable containers:

[0127] a) To reduce the nitrate content:

[0128] 20 g/100 l to 200 g/100 l water, preferably 60 g/100 l to 120/100l water.

[0129] b) To reduce the ammonia, nitrite (and nitrate) content:

[0130] 50 g/100 l to 500 g/100 l water, preferably 100 g/l to 250 g/100l water.

[0131] The uses of PCL granulated material described above mixed withthe bottom layer and in aerobic filter systems require a certainmaintenance expenditure and comprise a partially undesirablemanipulation with first use or subsequent dosing:

[0132] a) The PCL is gradually degraded by oxidative microbiologicalprocesses over a period of 6-12 months. The reduction of the nitratedegradation efficiency resulting therefrom requires a subsequent dosingwhich is, in part, inconvenient to handle.

[0133] b) In particular the subsequent dosing into the bottom layer isnot easily accomplished in an established aquarium.

[0134] c) To maintain or correct the nitrate degradation efficiency, thenitrate content of the water should be measured at specific intervals,e.g. once a month, to maintain or increase the desired nitrate reductionby a subsequent dosing in the event that the nitrate concentrationincreases again.

[0135] These handling disadvantages may be avoided by the alternativeagents and processes described in the following.

[0136] Use of PCL Powder as Nitrate Reducing Water Additive:

[0137] If one uses the substantially more reactive PCL powder instead ofthe PCL granulated material and simply adds the powder to the containerwater in periodic dosages, then it is surprisingly found that thistreatment results in a reliable, dosage-dependent and permanent nitratereduction.

[0138] In this case, the weekly dosing of PCL powder is fullysufficient.

[0139] The PCL powder which is added to the container water, insolublein water and merely suspended, is partially absorbed by the filteringsystem and reaches between the bottom particles (sand, gravel) in partto there activate the nitrate reduction under largely aerobicconditions, the results of which are described in the following.

[0140] Introducing Various Dosages of PCL Powder Into the ContainerWater.

[0141] The following amounts of PCL powder are added once a week toaquariums with current container conditions and average plant and fishpopulation and easily mixed with the water:

[0142] a) 0 mg/l PCL powder (control)

[0143] b) 5 mg/l PCL powder

[0144] c) 10 mg/l PCL powder

[0145] d) 20 mg/l PCL powder

[0146] The following dosage-dependent nitrate concentrations wereascertained over a test period of 24 weeks:

[0147] a) (Control) Constant nitrate increase from 23 mg/l to 232 mg/l.

[0148] b) (5 mg/l) Nitrate increase from 22 mg/l to 74-76 mg/l after 12weeks, then no further increase in nitrate up to 24 weeks.

[0149] c) (10 mg/l) Nitrate increase from 22 mg/l to 43 mg/l after 24weeks. An intermediate maximum of 54 mg/l was attained after 6 weeks,followed by a decrease of the nitrate content to 43 mg/l.

[0150] d) (20 mg/l) The nitrate content decreased over a maximum of 38mg/l after 4 weeks to 6 mg/l after 24 weeks.

[0151] It was concluded from the experiment that a dosage of 10 mg/l PCLpowder per liter of water which is appropriate in practice is sufficientto prevent the nitrate content from increasing to more than 40-50 mg/lover long periods.

[0152] Significant advantages of the new process according to theinvention are the simple handling (simple dosage of the recommendedamount, once per week) and the maintenance and control-free nitratereduction over any long periods.

[0153] By varying the dosage, the desired, sustained stable nitratelevel can be adapted, e.g. also to the population density with fish.

[0154] Dosage of 10 mg/l PCL Powder in Various Water Conditions:

[0155] The weekly dosage of 10 mg/l PCL powder deemed appropriate inpractice was subjected to a long-term test under various containerconditions. The carbonate hardness (KH) of the water was varied.

[0156] The following experiment was performed at KH 2° dH and KH 11° dH.(Length of experiment—20 weeks)

[0157] Once per week, 10 mg/l PCL powder was added to the experimentalaquariums with current container conditions and average plant and fishpopulation which differed only in the water chemistry (KH) and lightlymixed with the container water. The following nitrate concentrationswere measured over the test period of 20 weeks:

[0158] a) Soft, mineral-lacking water (carbonate hardness: about 2° dH)

[0159] Control (without dosage of PCL powder): continuous nitrateincrease from 2.5 mg/l to 150 mg/l after 20 weeks.

[0160] With the same PCL dosage of 10 mg/l, the tested PCL variants onlydiffered in the concentration of carbonate hardness additive which hasno affect on the nitrate degradation.

[0161] Variant A (10 mg/l PCL powder): from 2.5 mg/l over a maximum of25 mg/l after 6 weeks, the nitrate content fell to 10.5 mg/l after 20weeks.

[0162] Variant B (10 mg/l PCL powder): from 2.4 mg/l over a maximum of26 mg/l after 8 weeks, the nitrate concentration dropped again to 14.3mg/l.

[0163] b) Medium-hard tap water (carbonate hardness: about 11° dH):

[0164] Control (without dosage of PCL powder): The nitrate concentrationincreased continuously from 25.5 mg/l to 170 mg/l after 20 weeks.

[0165] Variant A (10 mg/l PCL powder): from 25.4 mg/l NO₃ ⁻, the nitratecontent increased to a maximum of 30 mg/l after 3 weeks and then droppedcontinuously to 14.3 mg/l after 20 weeks.

[0166] Variant B (10 mg/l PCL powder): from 25.4 mg/l NO₃ ⁻, the nitratecontent increased to 32 mg/l after 3 weeks and then dropped to 12.4 mg/lafter 20 weeks.

[0167] Use According to the Invention, Types of Application:

[0168] The use of PCL powder for nitrate reduction in container watercan take place in various application forms:

[0169] a) Pure PCL powder in dry form. A measuring spoon may be used fordosing and measuring.

[0170] b) Aqueous suspension of PCL powder in defined composition.According to the prior art, known suspension stabilizers are added tothe suspension, e.g. a thickening hydrocolloid. Example: Xanthan in asuitable amount. The amount of suspended PCL powder in the product isdetermined from the product dosage, e.g. in a milliliter of productsuspension per 4-liter container water and the desired dosage of PCLpowder.

[0171] A typical example is an aqueous, stabilized suspension containing40 g PCL powder per liter. To obtain a weekly dosage of 10 mg/l PCLpowder in the container water, 1 ml of the suspension must be added per4 l water.

[0172] c) Aqueous suspension of PCL powder in defined composition towhich further functional additives are added. It was shown to beespecially advantageous if PCL powder and a suspension stabilizer wereadded to a multifunctional liquid product, as described in WO 01/21533.

[0173] In addition to sodium citrate, citric acid, ferric citrate,citrate complexes of tracer elements and B vitamins, saccharose, 40 g/lPCL powder were added to the product solution. The addition of PCLpowder significantly improves the nitrate-reducing effect of themultifunctional product described in WO 01/21533 and as a result alsoimproves the attainable water quality to a previously unknown degree andcompletes the effective spectrum with a very good nitrate degradation.This improves the product considerably and makes it possible to omitchanging the water in the aquarium over long periods (also more than 6months).

[0174] Summary of the Process Based on PCL Powder:

[0175] 1 mg/l to 100 mg/l, preferably 5 mg/l to 20 mg/l of PCL powderare added to the container water periodically, e.g. daily, every 2 or 3days, weekly, every 2 weeks, monthly, preferably weekly.

[0176] The agent of the invention can be PCL powder itself and/orcomprise all feasible, PCL powder containing preparations which arefunctionally and technologically appropriate and feasible, e.g.

[0177] aqueous suspensions,

[0178] suspensions in other functional liquid products, e.g. such asdescribed in WO 01/21533,

[0179] pasty preparations, etc.

[0180] The preparations may contain any additives desired, e.g.suspension stabilizers, thickeners, colorants and odorous substances andalso substances according to the prior art.

[0181] As already described for the use of PCL granulated material, theaddition, insertion of PCL in container systems can also produce thereduction of ammonia and nitrite, in addition to the reduction ofnitrate.

[0182] When using PCL powder, corresponding concentration reductions ofammonia and nitrite are also observed with comparable effectiveness.

[0183] In this case, increased dosages of PCL powder, e.g. 10-100 mg/lweekly, preferably 20-80 mg/l weekly, are shown to be especiallyadvantageous.

[0184] Use of Further PCL Application Forms Having a Large Surface:

[0185] The use described above for reducing nitrate with the extremes,PCL granulated material having a relatively small surface, on the onehand, and PCL powder with an extremely large surface, on the other hand,makes it clear that all feasible application forms of PCL, the surfaceof which is similarly large as for PCL powder or lies between powder andgranulated material, are also suitable for use in container systems toobtain similar, comparable effects.

[0186] In addition to the application forms already described in thefirst application or technologically appropriate production variations,PCL may be used in other variants, especially with a large surface, incontainer systems to reduce the concentrations of nitrate and alsoammonia and nitrite, e.g.

[0187] as fleece, fiber webs,

[0188] as foam of various pore sizes, e.g. ppi 5 to ppi 50, the PCL foambeing produced according to conventional methods according to the priorart,

[0189] as PCL coating of materials having a large surface, i.e. asapplied PCL layer on mineral, organic-natural, organic-syntheticmaterials,

[0190] as PCL coating of porous materials (organic, inorganic) byplacing thin PCL layers onto and into these materials, as fine foilleaf,

[0191] as thin PCL coatings on any unnatural, non-living decorativearticles in aquariums, e.g. on stones, roots, figures,

[0192] as thin PCL coatings on plastic plants, filter wadding.

[0193] Thin PCL coatings can, for example, be produced by dipping,immersing the materials in liquid PCL (FP≈60° C.!). After cooling, theimmersed materials harden the PCL film to form a thin, solid coating.

[0194] The dosage of PCL in the described application forms having alarge surface is 1 g to 200 g per 100 l water, preferably 10 g to 100 gper 100 l water, in the container systems, e.g. aquariums.

1. Use of polycaprolactone for the aerobic removal or reduction ofinorganic nitrogen compounds from or in biological container waters. 2.Use according to claim 1, wherein the inorganic nitrogen compound is anitrate.
 3. Use according to claim 1, wherein the polycaprolactone isworked into the bottom while maintaining aerobic conditions.
 4. Useaccording to claim 3, wherein the polycaprolactone is worked in asgranulated material.
 5. Use according to claim 3, wherein thepolycaprolactone is worked in in a quantity of 20 g to 200 g per 100liters container water.
 6. Use according to claim 4, wherein thepolycaprolactone is worked in in a quantity of 60 g to 120 g per 100liter container water.
 7. Use according to claim 3, wherein the bottomlayer consists of gravel having a particle size of 1 to 8 mm.
 8. Useaccording to claim 7, wherein the bottom layer consists of gravel havinga particle size of 3 to 5 mm.
 9. Use according to claim 1, wherein thepolycaprolactone is added to the container water in powder form or as asuspension of a powder.
 10. Use according to claim 9, wherein thepowdery polycaprolactone is added to the container water in the form ofa pasty preparation.
 11. Use according to claim 9, wherein the powderypolycaprolactone is added to the container water in an amount of 5 to 20mg/liter water.
 12. Use according to claim 11, wherein the powderypolycaprolactone is added to the container water in an amount of 10mg/liter water.
 13. Use according to claim 1, wherein thepolycaprolactone is worked into coated large surfaces to produce theremoval or reduction in aerobic working conditions.
 14. Use ofpolycaprolactone to produce agents for the aerobic removal or reductionof inorganic nitrogen compounds, in particular nitrate, from biologicalcontainer waters.
 15. Use according to claim 14, wherein the inorganicnitrogen compound is a nitrate.
 16. Filtering agent for container waterfilters containing polycaprolactone under aerobic conditions. 17.Filtering agent according to claim 16, consisting of a homogeneousmixture of filtering agent and polycaprolactone.
 18. Filtering agentaccording to claim 17, wherein the polycaprolactone is added to thefiltering material in an amount of 25 to 75% by volume.
 19. Filteringagent according to claim 18, wherein the polycaprolactone is added tothe filtering material in an amount of 50% by volume.
 20. Filteringagent according to claim 16, wherein the filtering material is gravelhaving a particle size of 2 to 5 mm.
 21. Filtering agent according toclaim 16, wherein 20 to 250 g polycaprolactone, preferably 60 to 120 g,are contained therein per 100 l container water.
 22. Fleece filter bagcontaining a filtering agent according to claim
 16. 23. Use ofpolycaprolactone to produce filtering agents according to claim 1.